scratchy sound from tweeter

Hi everybody reading this. Love music but have not a clue about electronics. Since my arthritis stopped me from playing piano and guitar I now listen to vinyl from my old vintage system. Fisher Studio Standard - CA-880 and small Relistic minimus speakers. I bed you laugh now but hey - I am on a small retirement budget.

Sometimes I like to crank the music up (loss of hearing helps doing so). Now a problem occurred while listening. Mostly the left speaker makes a scratchy sound especial when volume goes up.
But there is also a bit scratch in the right one but about 90% less. I changed to wires to reverse left and right speaker to check.

I first thought it could be the 1980's amp condensers. (They might could benefit from a replacement too)
Since the left speaker was observed to have a problem I changed the tweeters in both speakers.
But the problem is still there. It feels when the amp gets warm it increases the scratch.
Question: Is it possible that only the crossover in the left speaker is bad ???
Thanks upfrontPuu
That amp puts out 100 Wpc. Awful lot for those little speakers. Played loud enough long enough you may be hearing voice coil damage. Common symptom, plays fine at low volume, noise gets worse as the volume goes up and the cone excursion increases.

Simple test, take a battery, touch the speaker cables which will make the speaker move in or out. Which way the speaker moves depends on which way you hold the battery. One way it will go in, the other way out. There may be a bit of a pop but it can't hurt anything, battery being much less voltage than your amp has been putting through them.

What should happen if everything is fine is the cone moves one way with almost no sound and goes back when you let go. Flip polarity and the cone should go the other way. If its quiet then your speakers are fine its something else. But I suspect you will hear a scrape or something indicating the speaker (woofer, you already replaced the tweeter) is on its way out.

Mahalo Millercarob for your speedy reply and detailed instructions - highly appreciated!!!  Will check soon.

Sounds like you know the amp. I misten thought it is 80 w since I  picked somewhere up, the 880 uses two (one for each channel) STK-0080 power amplifier paks, and they are rated at 80 watts.You are right, all happened after I cranked the amp up to the edge of distortion. My mistake and I regret, but still love the nice blue

vu meters on them ....

As suggested, I took a 9 volt battery from a remote and tested.

Only on first contact I hear a static sound and see the bottom speaker membrane move (depending on polarity) in or out. No sound there.
I cannot observe a membrane moving at the tweeters.

I also tested the old tweeters this way, one is making a static sound on first contact and one does not make any sound.
Can the crossover be blown or is something bad in the amp???
Voice coils are rubbing against the magnets! Turn down the volume before the damage is permanent!
One of the 8 inch woofers in my Snell E's now does this all the time! So I had to buy a replacement pair from SEAS! Careful with that volume control!
You can find a pair of ADS 200 speakers available for not much money! Same size and configuration as the Radio Shacks. But much better build quality! USA - built! 
You know, if those are ferrofluid tweeters, it is quite likely the fluid has vanished, and the coils are covered in gunk. 

See if those speakers were in fact ff tweeters, in which case you can do the repairs yourself. 
Thanks so much to you all here, I feel blessed and like to express my gratitude!

I tested the speakers with a 9 volt battery and reverse polarity. They pop in and out without any noise besides a static crack when connecting.
Next thing I will do is to test the Fisher with different speakers. Have to drive two hours to a friend and will update my testing here.

Thanks for the suggestions, that fit my budget . Since a work injury took me down 13 years ago  - I shop @ thrift stores.
In my old working life I rode a bike an skipped a car, this way I could effort a Linn system (LP12, LK1 LK2 and Linn speakers) and I was a happy camper for many years.
That life is gone and I miss parts of it. But the CA-880 made listening to Oscar Peterson "You look good to me" still a pleasing experience, clean and a bit punch. And yes, the Realistic speakers lack a lot and I came close to add an SVS sub to them ( I hat to let go of a "housing only" damaged pair for a great price due to high shipping cost).

Mahalo for your input!
I tested the receiver with headphones and different speakers - all is fine.
Anyway, after a long music journey (like many of you may have done – the first “furniture” to plan to position in a new home where my speakers) I now consider to slowly upgrade my baller system, starting with new speakers! (Guess I am still hooked and I miss my old Linn system remote as a comfort queen)

Well aware the budget guys pay always double; I have to wrap my head around replacement, the $ 60  Dayton Audio B652 and add a Dayton sub or yield at the Pioneer SP-BS22-LR for $100.

A bit much, but I would love to yield at the ELAC Debut 2.0 B6.2 for $277.00 a pair or the KEF Q100 for 320.00. Never heard them and wonder if I can trust the hype.

The Ca-880 has no special sub connection to put out the right crossover signal (hope I say this right?) and I question how the ohms for sub and speaker will be ok fro the CA-880 and future amp.