Radio squealing.

[KD0PLC]

This question isnt about hams but since it is about radios i figured this is a good place to start.
I have my grandpas CB in my car right now (Uniden Bearcat PC68XL) and when i transmit most of the time all people hear from me is a squeal. Im hoping to fix this because its irritating to me knowing i cant be understood and annoying to people who hear it. Ive tried other mics so thats not the problem but heres some info on how its hooked up.

Power run from a 10 amp turn signal fuse and grounded to a screw on the fuse box (I think this is the problem and am planning on running it to battery)
Antenna is a cobra HG-A1000 21 inch base loaded whip stuck in the center of my trunk.

Any info or advice would be awsome!

[WB2WIK]

I don't know if there's enough power available where you've tapped in, or not, but generally the rig should be grounded at its mounting bracket (to automobile sheet metal).  If it's a temporary installation that may not be possible, but it should have a solid ground connection to the vehicle's frame somewhere, even if that is at the end of the power cord.

The antenna right behind the rear window might also be causing a problem.  Can you try the same antenna (if it's a magnetic mount) in the center of the vehicle roof, instead?  Less likelihood it will radiate back into the mike cable that way, as you'll be "shielded" from the antenna by the roof.  It's also likely to work better up there.

A 21" whip on CB is really heavily loaded!  That's only 0.05 wavelengths, kind of like using a 4" long whip on a 2 meter rig.

[KD0PLC]

Alright ill try those and get back to you tomorrow on if that was the problem.
Ive read places that it could be mic feedback and that would make sense that the antenna is radiating it back at me.
Thanks for the tips

[K1CJS]

Are you using the stock mike--or did your grandfather put a 'replacement' mike on the rig?  If the mike is a replacement, its output may be turned up too high, or the battery in the thing may need to be replaced if it has one.  All too many times people put those 'funny' mikes on their CBs, didn't really know what they were doing, and ended up overloading the transmitter section of the CB.

[KA1MDA]

Does it squeal all the time, or just when the engine is running? If the squealing goes away when you shut off the engine, it could be alternator noise.

Tom