Incoming sound Muffled

Is it everybody, or someone running a high amount of power?
Try turning the rf gain down when you are close to them and see if that helps.
Sounds as if they are overloading the receiver

 

Put an external speaker on the radio, if it sounds better, then the speaker is blown - it happens.

 

I wonder if the front end of the radios are getting blown out. Do you have another antenna near the CB antenna for another radio that you transmit on? Or are you in an area where someone is running a ton of power close to you?

 

Recap:

Since it's both radios, we can assume that it's not a problem with the radio. It's unlikely (though possible) for two radios to develop the same problem at the same time.

Invoking the "gazinta-gazouta" method of troubleshooting:

One thing "gazouta" the radio; the audio, which sounds muffled. You've stated that both the internal speakers and an external speaker all do the same thing.

Two things "gazinta" your radio; DC power and RF. I'm assuming that your truck is running OK, so your DC voltage is good. You didn't mention transmit problems, which reinforces that. That leaves RF.

The antenna seems to be OK, also due to the fact that you're transmitting and the antenna light is not on. Regardless, you should be able to receive just fine (short range, though) with just a random piece of wire stuck into the antenna jack.

That leaves the signals coming into the antenna.

It's been my experience that current CBs dont' have very good receivers. Couple that with the fact that most truckers' CBs put out a really crappy, overmodulated signal, I'm not surprised that the close by people sound lousy. When you hear it happening, turn down the RF Gain control on the radio, and see if it clears it up.

What it sounds like is a close transmitter is overloading the front end of your receiver. Normally, the front end can filter out all the "splatter" products of overmodulation, but not with an overly strong signal.

When I first got my truck, I borrowed a CB from a relative. (Name brand, currently on the market.) The signals on the air sounded so bad that I only turned it on when needed (at a stop, find out the cause of a backup, etc.). On my next trip home, I brought my $1200 ham radio with switchable filters. With that, everyone was at least understandable. I picked up a Uniden 980SSB a couple months ago when they were on sale at Love's. Even though I don't care to use SSB on CB, it has a better receiver than the AM-only radios. It does a passable job of filtering out the crap.

Now if I could only find a filter that tunes out echoechoecho....