radio interference with transmission/reception with Solo 2625-01running

I own a Ventus 2CXM built 2007 with a factory installed Walter Dittle
FSG 2T radio. I use the Sennheiser headphones (factory installation)
during the engine running procedures. Unfortunately, I have always
had severe interference with the radio tramsmission/reception during
the engine run. During the engine run, whether idle or full power,
the reception is weak and garbled with a great deal of backround white
noise. My transmissions are totally garbled, weak, and
uninterpretable even to other aircraft 50 yards away. When the engine
is not running I have not problems and my fellow pilots report that my
transmissions are strong and clear. This is becoming a safety problem
while taxing onto the active runway, as our glider airport is now very
busy with power traffic and a new flight school. Has anyone
encountered this problem and know of a list of things to check before
sending the aircraft to an aviation radio specialist?

John Iacobucci
Grand Rapids, Michigan USA
+1 (616) 485-3980