Here's the situation:

Lady is hearing lite thumps under floor.
Sometimes for 5 mins, and 5 seconds other times, always in same 8 ft area. No pattern, just random.
DOES NOT HAPPEN EVERY DAY. Maybe 3-4 times/week.

I crawl under, find no fresh droppings of any kind, also find that floor goes to walls.
So, thinking nothing can come from above..like attic.
Small holes and wireless vent grates are large enough for a squirrel or chipmunk.
So I set cages outside and tube traps underneath, and large sticky pads underneath.
No catches for 5 days.

Any ideas/input is appreciated

Thanx

Call Ghost Busters....

Repair all the holes and leave one open and make funnel set over the hole . I made this one yesterday
http://www.youtube.com/watch?v=5PjQo0dbUCo&feature=youtube_gdata_player

Any plumbing under there? Pipes can sometimes vibrate or rattle when a tap is opened a litle bit or if the toilet filler valve is fluttering.

I did this one job when I first started . The lady complained about a noise in her wall . I looked under and over all around but stopped short of cutting a hole . She kep calling me . It's back . I tried and tried to solve the problem . Trapped a few mice but still it kep coming back . Finally after like 6 weeks I herd the noise to . It was also windy that day . What it was is where her phone lines came into the house that little plastic O ring had worn out and that made it make the sound she was hearing . This spring I got a call and it was her wind chims making the scratching sound . Last summer found a loses chimney flue making a crazy sound . I learned good from that first job . It's not always a critter .