Fan on Amp Unbeatable

So, I have an older amp from the 70s. It's a solid state amp and the fan is so loud it's distracting. It's my first largest solid-state amp. I've been using tube amps for the last 15 plus years. I can't imagine fans are supposed to be overwhelming Lee loud. Has anybody else ran into this kind of issue and if so, how did you fix it?
Depends. Some run whether needed or not. If not then simply disconnect it. My Dynaco was like that, a simple socket mod let me leave it unplugged most of the time. Usually need to be driving them pretty hard to really need a fan. If it really is needed then remove it. Hopefully find something with a part number on it. Because unless you are lucky enough to find its a simple clean and lube then its gonna be replacement time.
Fans in SS power amps are because the designer was cheap when it came to heat sinks.

That is why there are so few with fans.
I have had a few Pure Class A amps that got extremely hot and had fans.  I replaced the fans with high speed quiet fans,  then used resistors to slow them to a tolerable point for noise.  My amps lasted and lasted.  You might try that. 
If the junction temperature exceeds 90 degrees C, your output transistors will have very short lives. You could monitor their case temperature with an inexpensive (read somewhat inaccurate but close enough for this purpose) IR non-contact thermometer. Refit with better heat sinks and use computer grade thermal compound. 
You know, fans are quieter, especially when new now. :) Cheap too.
You may be able to replace the fan with a fan exactly the same size that is quieter. Digikey and Parts Express have hundreds of them. Measure the voltage on the fan leads it is usually 110 VAC or 25 VDC. If 25 VDC you can wire a pot to it to adjust the speed then as Sleepwalker suggests track the temp on the heat sinks. I have had several amps like the Krell KMA 100 that had fans you couldn't hear.  
I used the 5” battery powered O2Cool external fan for both Bada headphone amp and Woo Audio headphone amp. Just point the fan at the tubes and let er rip! Problem solved! 11 bucks on eBay, fast n free!
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My home theater amp (Lexicon LX-7) has a fan.  I took it in for service for another issue and asked if they could put a quieter fan in while they had it.  It's much quieter now.  I can hear the fan if I put my ear within about a foot of the unit, but beyond that it's inaudible.  
Hmm will try some type of nose muffler first. Need to be careful of not allowing airflow. Any other solution involving opening the case will have to be done by my tech. $$$$. :<(
Go here:

I’ve got a 5" side discharge on my tube pre-amp and it keeps it very cool. It has three speeds. On low you can hear it when you are next to it, but not across the room.

My SS amp has enormous heat sinks but I might put one of these on top of each one anyway.

The company makes thermostats for their fans as well.
I had an original Ampzilla with a noisy fan....turned the volume up.
“I have had several amps like the Krell KMA 100 that had fans you couldn’t hear”.

I still miss my KMA100s after all these years, my first true high end purchase back in the 80s
spinaker yes they were very special back then. Unfortunately those output transistors ran hot and many of them eventually blew their output stages. Like a light bulb turn them on and off a lot and eventually.....
Another idea to consider: take two of the largest diameter DC fans you can find, the larger the better. Wire them in series to a large enough DC wall-wart of the same voltage as just one of the fans and go for 50~100% over the current draw of just one.  Pad the bottom (intake) sides of the fans with soft weatherstripping foam to isolate vibration from the fans, and lay them over the top of your amplifier above the heat sinks. 

I did the above with an old receiver many years ago, and it kept the amplifier section from overheating, even when driving hard loads at high volume levels. 
I did something like sleepwalker described with my home theater processor and my Peachtree Nova 300, except I used a usb fan. You should be able to connect the usb fan to a phone charger with a usb outlet. 
Anyone wanna buy a noisy Marantz 500?
If you are serious about selling your Marantz 500, they are currently asking big bucks for them right now. Go look on the bay. Many of them go overseas ( I do not know why ), but they do.
@pawlowski6132 - I can't stand any audio equipment with a fan. The noise reduces the S/N ratio tremendously.
If your amp really is worth big bucks (as @mrdecibel says), my suggestion is, sell it and start fresh. There are a lot of great modern SS amps around, and very few have fans.
@mike_in_nc : "The noise reduces the S/N ratio tremendously."

Ah, it had to come out. How can those who obsess about power scrubbers, springs, ceramic feet, power cables and aluminum foil hats not be appalled by whirring electric motors with blades next to, on top of or inside their multi-thousand dollar components that can't keep themselves cool enough to survive in typical climate controlled homes?
I've used laptop coolers to set the equipment on. Mine had funky lights which were promptly disabled. I think they had adjustable speeds also.
FWIW, I just opened the top to see if I cold easily disconnect the fan. Amp is now for sale on Audiogon.
I set one of these on top of my AR LS-16 tube pre-amp and it really keeps things cool even on the lowest fan speed:

So, I bought two of them to set on top of my solid state Proceed HPA2 amp. It has two huge heat sink openings that draw from underneath.

With the two fans on low the aluminum heat sink hardly even feels warm.

So the question is this: is there any chance of a SS or tube component running too cool?
What a clever little fan @n80! I'm gettin' me some.
I chose that particular model because my components are in an open front console without enough clearance for an upward venting fan.

You can also get a thermostat module very inexpensively if you feel like you need it. Mine do great on the lowest setting so I don't see much of a need.

I probably don't need them at all but my listening room is a converted sun porch and the HVAC is not as effective in here and it runs 4-5 degrees warmer than the rest of the house in summer. 
stringreen..... ma man!
To fan or not to fan....I keep my SAE 502 on wood blocks which keep the preamp off of it by like 2 problem.