Anyone buy and use these from Ebay? I got a 636 that makes scratchy sound when keying up. Tried cleaning contacts. After a short while the scratchy key up returned. I can hear it in the talkback. Every once in a while someone comments on it. Also have and old RK 56 that does not seem to be as loud and punchy any more. It has a new plug cord and chrome case. Get better compliments from the 636 and a SRA 158. Any comments about mic repairs and Ebay products /vendor's.