The bass of my radio is feeding back thru my cb radio

if your radio has mic gain it may be that its turned up to high and it will cause feed back.

is it used? if so it may have been hacked for more channels and no one finished the work.If its new send it back to cobra .its under warrenty

Change Mics and cord.

always check the swr's first before installing radio

When you shorted the CB ant cable, you may have burnt the ground wire in the headset connector

Have your antenna checked at a place that knows what they're doing. If your antenna system is bad, ground problem,coax bad mount or maybe just a wrong or bad antenna. Then the sounds not getting out the antenna and its feeding back thur the radio.If your echo board was bad then your radio wouldn't transmitt at all.
If you unplug your external speaker will it squeal? If not do the antenna and if that reads fine just try a better speaker like a uniden 20watt speaker.I own a CB shop and this is easy to fix.

Its just RF feed back, that's normal, try to re-route the coax, or just turn the FM down, o try turning your modulation down....hope this was helpful....

have your antenna checked, the powers not getting out the antenna so its feeding back thur the radio

Turn off the talk back, make sure the echo is not too much, back the mic gain a bit.

that is called feed back turn down your mic gain and it will stop squelling when close to others.