AC "Hum" from Radio Speakers

Just wired a new radio in our TM. When operating without AC power and using only the the battery, the radio sounds great. However, when plugged in to shore power there is an added hum to the speaker sound. I expect this is feedback noise from the converter. Any suggestions how to resolve this problem? Does the 7300 series provide filtering to eliminate the hum?
Lastly, are the 12v sockets disabled when using shore power?

Wade

You just need to add an inline filter....it's the same one you put on one in a car, they're not very expensive, and can be had at any auto parts store such as advance or auto zone. Simply wire it into the main power line between the radio and the battery........

Happytrails......

I agree with Happytrails.

I had a hum like you described in my first car (1970 Maverick).  

The ignition system was not designed for the sensitive electronics of the 80's....

An inline filter fixed the problem.

Thanks to Happytrails and Oilspot for the inline filter tip.
I'll get one and try it. Installed a combo MP3, Radio, CD, plus DVD player all in a single din size slot. Also has a remote. Hardly roughing it I know, but fun nonetheless.

Wade