"busy" symbol

I am using BH 2.0.4 - largely Ten Below's backup with a few additions. Recently the twirling symbol in the upper left hand corner (which in my mind equates to the busy symbol in Windows) has been coming on pretty frequently (sometimes every 5-10 mins) and staying on for up to 30-60 secs. Whilst the viewing never misses a beat - either watching TV or a recording - it's beginning to annoy me. Any ideas what it might be, and is there a way of finding out / stopping it?

Thanks.

Thanks for helping on this.

The response to "top" maybe suggests that memory maxing is not the problem. It keeps changing, but the most common response seems to be:
tasks: 95 total, 1/2 running, remainder sleeping
cpu(s): 0.3%us, 0.5%sy, 0.0%ni, 97.4%id etc.
Mem: 571980k total, 201864k used, 370116k free, 204k buffers

I can't pretend to understand it all, but it looks like cpu is largely idle and memory is less that 40% utilised?

Maybe you can make more sense of it, or suggest something else to look at. The annoying thing is while the "busy" symbol (not sure exactly what its correct name is) is active, the picture never misses a beat, but I cannot initiate any action from the remote.