is the chassis earthed? I've had to do 2 systems for first time ever in eternity of IPO. 8.0.44 with ATM combo cards on both, funnily, calls to Vodafone mobile network were horrendous on one of the systems, sounded really awful.
Electrician actually fixed an earth properly to the data cabinet, linking wall bracket part to swinging cabinet part where IPO mounted, and problems disappeared.
levels all became nice again too across all trunks.
handsets were mix of 1403, 1408, 1416 and analogue handsets.
Then similar thing happened week after, immediately used earth wire to the chassis mount position on back of control unit, and no problems hey presto.
Cheers,
Chris