Ron and all,
the AT-300's with the 9 volts. (not your AT-3000 series that have the "AA" batts) have a similar situation that the metal contact spring problem in them that after about a year of nightly use (and i mean 365 - 400 shows),
they start to start having contact problems with the battery ans sound like they are being interfered with. although the real problem is that the contacts have become compressed. the only acceptable solution is to get the contacts replaced.. bending them out to make a better contact has broken a few by a few KJ's that have used my rigs.. and the fix isn't that expensive.. it's alot less expensive than replacing a whole microphone or wireless system. but it's a major pain if it goes out when you don't carry a wired mic as a back-up i carry 3 real good Wired back ups in each system and a personal wired and a phantom powered condenser headset (48v). in my personal system ( depending on the show) alot of times i'll never use it. a great sounding wired handheld is just enough for me.
But Ron is in the right direction and is on to something.. and has a great system that works for him. His system is very simple and Does it very effiently. his show is worth a look.
Brian D.