I recently used a Sony wireless lav (with UTX-B1 transmitter). The system was attached by my Edirol Fa-101 interface to my laptop for direct recording. Monitoring through a Sony MDR 7506 head-phone. There was an audible high pitched hum along with the transmitted dialogue, and I did not know where it was coming from. I then tested the system with other mics with no hum (i.e. AT897, AT825, Marshall v76 all hardwired instead of wireless). So I am fairly certain it is not the rest of the equipment (though not absolutely certain). BTW, all testing and equipment was in a 15x20 room (just in case it matters). What, if anything, can I do to reduce this problem? If I can't reduce or eliminate the problem can I use noise reduction or something else to fix it in post (note I would rather get clean sound in the first place than have to fix in post, but if need be I'll do it)?

I have never experienced such problems with my kit, same model. Were you close to any CRT video monitors? Was it 15 KHz? Perhaps the weak link might have been the small cable that connects the receiver's output, it might have been picking up EMI from a nearby CRT.

I was in a fairly tight space (for testing purposes). I will try it again in a more open setting. But if that is the problem, then I am stuck for no lav on nearly half of my shoot.

> then I am stuck for no lav on nearly half of my shoot

No way. If the problems persists, contact Sony and have them replace the kit. First, try it with another preamp or camera though. Perhaps the interference was camera-originated.

Ok, maybe I'll get lucky, but somehow I think I'll be calling Sony. I'll keep you all posted.