Help identifying Tuner noise

I am receiving a specific noise that is continuous when it occurs and sounds like "Locusts" in the background. Otherwise, the sound is excellent with a strong signal. The noise is also intermittent, so it comes and goes but I can't pinpoint it to a specific time of day. I've noticed the sound on two or three stations, so not all stations.

I own a McIntosh MR71 tuner that is in excellent operating condition. With this tuner I use an SE Engineering Antenna with a rotor. When rotating the antenna, the noise will lessen as the station's signal drops out.

Any thoughts?
Simple. Either the tuner is not sensitive enuf to pick up a weaker signal, usually coming from a distance station, or the station is broadcasting a weak signal to begin with, or both. I have both a weak station and a tuner (Perreaux) with less than optimum sensitivity and on that tuner I have a constant hiss on all but strong signals from close stations. On my Accuphase the same stations are dead quiet. Not much you can do about this that you haven't already done except, perhaps, move your antenna or try an antenna signal amplifier but I doubt that either will work as any benefit this might bring would really be minimal.

Note the differences you see on your tuners meter which measures signal strength as you go from station to station and note how this correlates with the noise factor.

One thing you can do, if the station is important to you, is to press the mono function button. This will make most of the noise go away, but you obviously get a mono signal.

Maybe someone else has some ideas, but I hope that will help.
Thanks Newbee, but I'm getting a strong signal and my Tuner is very sensitive. It's not hiss, and it does sound like in you're in a field of locusts or maybe cicadas. The intensity of this noise varies, and right now it's gone!

I've done all the internal tests for related equipment, power, transformers, dimmers, furnace, washer/dryer, cordless phones, and wireless network. The sound is also present whether muting is switched in or out, but the sound does disappear when I switch to Mono.

Earlier, when I switched Muting in, the noise got louder and when I adjusted the muting sensitivity control on the back, I was able to get rid of the noise, I thought. Later, the noise would come back with muting in or out...then there would be no more noise.

I have been wondering if there's some kind of external interference causing the problem, but I don't know where to begin or how to test for such a thing.
The stereo decoder in the MR71 and MR67 (found in the slightly raised section on the front-left side of the chassis) is a bit prone to drift, and IIRC the symptoms you describe are exactly that of when the 38KC oscillator transformer is out of whack. But unless you're vary [sic] familiar with what you're doing, I would be VERY careful twiddling with it . . . a quarter-turn of the top core of this transformer is the most I would attempt without test-gear. Also keep in mind that the slugs in these transformers are very brittle, and they can crack very easily with an aggressive hand on a metal screwdriver.

You might also check the condition or substitute the tubes in the stereo decoder, otherwise get the unit professionally serviced and aligned. In servicing a vintage FM tuner, it takes a bit of experience to understand what types of adjustment are required just to age and drift, and what kinds of symptoms indicate that something else is going bad. There's also a mod available to the output section to provide a real separation trimpot adjustment, which can increase the separation performance by a good 5-6dB over the original.
Kennythekey, Simple minds = simple solutions! What do I know. Obviously not much. :-)

Sorry about that....................
No problem Newbee, I'm in the same boat!

Kirkus, thank you for the detailed and informative explanation. The tough part is that the Tuner was recently serviced, upgraded, and realigned by Sam Kim of Sam's Audio Labs, who's a guru especially with tuners. He thought that the tuner may now be too sensitive, and/or there may be an external source for the noise. Do you know where I can acquire that mod?

I will relay your explanation to Sam, so thanks again.