Before any definitive answers may be given you need to further analyze the problem and give us some useful information to work with, all I see so far are guesses based on an assumption. Here are a few questions not for you to answer here but rather aid you in tracking down the source of the problem.
Watching the bars on the signal strength indicator are you suffering from loss of signal?
If so, is it rising and falling, weak and fluttering to begin with or is the loss and re-acquisition sudden and drastic which may indicate a bad antenna connection?
Do you hear it only with mobiles or is the base station affected as well?
Do you lose audio while a strong, steady signal is present?
How about the squelch setting? It should be just high enough to quiet the hiss of an open channel with no signal present, if you have it up too high it will squelch the audio even with a signal present should the strength go down just a bit.
Do you have the problem with trunking, digital, analog or some combination?
These are only intended to give you some ideas where to look, you may have problems with your settings or any number of things. Once you have narrowed it down a bit you can give us something to go on, as it stands "chopping" tells us nothing at all. Then you may get lucky and fix it yourself once you have found the problem. A simple analogy is this; it's hard enough for a doctor to diagnose an illness over the phone and impossible when all he hears is coughing on the other end of the line.