Combines two way radio noiseIJ

for some reason, some machines have interference problems, IF the noise increases when the engine is started there is a 'interference kit' available from AutoZone, Advance, your 2 way dealer or the like that goes in the hot wire to silence the AC impulses which is the source of most interference. Inexpensive kit. A strong 2 way can also mess up some other functions of the electronics of the machine, make sure the antenna is above the roof level.

The noise starts when the key is turned on or in the acc position.It does not change when the engine starts.

Is it a high pitched whine or whistle or a hiss or whateverIJ Sometimes interference can come from bad brush _ commutator contacts in the cab's A_C fan motors. Try isolating the cause of the feedback by systematically switching off or disconnecting, one at a time, any items of gear that become live when you turn the switch on. As the noise occurs in the acc position, and does not change with the engine, this really limits the number of possible causes.

It sounds almost like a dail up connection or a little like a fax.Almost but not exactly.

I confess that I know very little about radios. I also believe that the USA still uses the CB bands. The UHF 40 channel system is used by everybody all over Australia with very little CB still used. So any suggestions from me are worth what you pay for them! If you have switched off or disconnected every thing else except the radio and still get the feedback then it is the radio and one of it's components that is possibly causing the problem. Does it occur over all channels or just around the channel you useIJ Try a different radio on your aerial system. A weird one which has occurred [very rarely] is that a part of a machine's electrical circuitry has become tuned to the frequency of a powerful local transmitter and then reradiates at a different lot of frequencies, in this case maybe yours! A completely different situation but as an old glider pilot, I actually received some radiation burns to my hand when about a half of a mile of winch wire, which is used to launch gliders a little like a kite on a string, became a huge aerial, tuned to the frequency of a close commercial radio transmitter tower, while I was being launched in the glider. The resulting powerful jolt made my eyes very watery and definitely got my undivided attention. It does happen. The reality is that your problem is probably something very simple. Finding it is the problem.The best of luck!