swiftsu, RX_QUAL is RX quality, RX_LEV is RX level, so I guess you know that quality and level are two different words, two different things, you may have signal with high level but it may have low quality (high amount of errors because of interference, HW problems)
If the signal is provided by a GSM repeater, the problem described by you can be due to repeater auto-oscillation (part of the signal comming out is “feeding” the input of the repeater) !!!
The problem can be corrected if the following condition is satisfied:
Antennas separation > Repeater’s Gain
So, either you increase the separation between the pick-up and donor antennas or reduce the repeater gain.
Most of the modern repeaters may have a AGC circuit (Automatic Gain Control).
I compair needing isolation between a donar and a serving antennas in a repeater, with when you hold a microphone too close to a speaker that it is broadcasting to. The mic picks up its own brodcast then it aplifies it and broadcasts it even louder, and again and again and again, until you remove the mic or shut down the amp.