If you are very close to the plane with your transmitter on, that could cause some. It should subside if you move away a few feet.

Radio interference from man-made or even natural sources is another cause. A bad crystal in the Tx or Rx, The wrong Rx/Tx shift/conversion/compatibility.

It really depends on what radio system you are using. FM? PCM/FM? AM? Synth? And wether or not you have the correct rx for the transmitter, etc.

There could be many causes....even something as simple as a TX that needs a tune-up.

There are some guys at our field who can help you better than I can. (I am just a newbie). You are close, so come on out any day but thursday and there will be an instructor who can help.

http://www.palomarrcflyers.org