Lag and phase shift while recording in Audacity

I use a M-Audio Fast Track C600 as an external sound card to record voice through a mic and my yamaha keyboard through audacity on my laptop.
I record the piece or track and when I listen to it i get these Bermuda triangle sort of disappearances within my track…as in the sound for 2-3 seconds in the track is replaced by this noisy buzzing sound. it is highly annoying because all of my tracks are peppered with such disturbances and it gets ugly when I try to record other instruments over it.
I don’t what it is called professionally that’s why I referred to it as a lag or phase shift. I think you’d understand my problem. Please HELP!

Loud bursts of noise can sometimes occur when using USB devices if there is momentary breakdown in communication between the USB device and the computer. Does this sound like the problem?

Generally you should avoid using a USB hub with a USB sound card - connect the sound card directly to the computer.
With full size computers, the USB connectors on the back may be more reliable than connectors on the front of the computer.
Try not to have too much stuff running at the same time as recording. As CPU usage increases, the likelihood of this type of problem increases rapidly.
Try to avoid using other USB devices at the same time (other than perhaps a mouse and keyboard).
See also:

on my laptop.

How big and old is the laptop? If you can’t make a simple recording, you’re never going to manage overdubbing sound-on-sound. That depends on perfect playback and record at the same time and critical timing settings to avoid latency and delay.

Has any of this ever worked, or you just took the shrink plastic off your Fasttrack? Do you DJ and is this the first time you tried to record?