Beeping sound coming out of left speaker?

Hi,
Need some help please.
Just recently I've been having these strange beeping sounds coming out of my left speaker every so often.It only lasts a few seconds and I've never heard it actually come out while music was playing until tonight.It sounds almost like morse code.I've never had any problems with my stereo setup until now and I've had it for about six years.I'm wondering if anyone has any ideas as to what could be going on? is this a normal occurrence? Thanks!