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I had a similar problem with a Uniden 520 recently. I took it to Justin to look at (I had gotten it used) to see if he could figure out why it would squeal with the KL-200p on. The problem was in the way the bonehead tech who worked on it originally had lowered the carrier for use with the amp. The mods were causing self oscillation on certain channels, which exhibits itself as squealing. He fixed it up and after a few minutes of repairing the junk mods, it worked great! Maybe the 510's you had were set up with the same type of problem?
Please advise me to what is a good replacement mic for my SR-497HPC... Answer: 497 is "wired like Cobra", so many choices available. That radio does not need a power mic, so purchase a stock "coffin style" mic with a decent cord, like the ones that Astatic uses. The Superstar DM-507 is my go-to. https://www.ebay.com/itm/3050474478...adANq91JSiEEnz8EGqPJRBloTgEyaVsBoCtoMQAvD_BwE $12.99 + .99 cent shipping.
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