Protect soundsystem from GSM/GPRS pulsing noise sounds
I assume by 'soundsystem' you mean either a PA (sound reinforcement) system, or a hi-fi system? The practical answers will depend on exactly what equipment you have but methods could include:


use balanced audio connections wherever possible
make sure all cables are correctly shielded and equipment is correctly grounded (earthed)
make any unbalanced connections, and those with low signal level e.g. microphone or turntable connections, as short as possible
if the source of interference is typically in one area relative to the sound system, try moving or turning the sound equipment in case this reduces the degree of pickup
if the equipment has an unshielded (plastic or wooden) enclosure, try replacing it with metal-cased equipment.