High uplink interference on idle, check Nokia BTS supervision counters (ZEEO:SUP;?)for exact details of your setup. The Iband level exceeded and duration will be in there.
External interference will not disappear if you reduce the TX power of the cell (ZEUG, PMIN 30 PMAX 30) Internally generated noise (intermod) will disappear or reduce significantly with a power down (ZEUG) We have seen issues with poor antennas/diplexors when mixing 2G and 3G signals. Antennas were always given a clean bill of health..