I have an KX-TA624 that I installed in my home with seven KX-T7030 phones. Two of the phones have the same problem. If you attempt to call them over the intercom from another phone and they're in the hands-free reply mode, you hear a loud growl in the calling phone. If the person yells, you can hear him above the growl. If he picks up the handset, the audio is perfectly clear. I have plugged a known good phone in this room and it works correctly. Other than replacing the two bad phones, is there a way to fix this problem?

A No! did you just hear what you asked you plugged in a known good phone and cleared the problem so its not the port the phones are bad either replace the defective phones or live with it

I guess I was looking for a component level solution, like replacing a filter capacitor or something common on the board. Thanks for the reply, though. I figured if two of the seven phones I have are showing the same failure, there might be a known internal fix available.

very few dealers will trouble shoot the phones to component level we send the to a refurbisher like
Usedphones.com

Try a can of compressed air on the circuit board. I've found that dust on the HF mic found in the base of the phone can cause what you described (at least it does on the brand of phone I service).

Like Bob said.. Probably a mic issue. Handset audio and speakerphone audio share the same components. A bad filter cap would cause buzz on hands-free and handset use. Unsolder 1 lead on the mic to see if the buzz is still there. Panasonic had an issue with moisture in the mics.

We've replace the mics on phones that have that problem. We take them out of other non-working phones. We always save parts