In article ,
k8vf-mark wrote:

my ic756 has an anomoly impressed on the transmit audio in SSB and AM.

Sounds similar to a pl tone, but much louder. Has about a 100 hz cycle
rate(guess).

It is louder when you turn up mic audio and compressor.

It shows up on the transmit scope, too.

Has anyone heard this and do you have any ideas on where to look?

It is not power supply related, btw.

Mark-

1. Microphone picking up sound of a fan.
2. Microphone magnetically coupling to power transformer or fan.
3. Bad shield connection on microphone cable.
4. CW Key plugged-in and keyed.
5. Monitor feature activated, providing audio feedback.
6. PL tone activated.

Try using the microphone as a "probe" to locate source of the tone.

Fred
K4DII