Clumping thymocytes?

[Allison]

I am at the cloning stage of my hybridoma protocol.  I plated out 
thymocytes as a feeder layer in a 96 well plate and then added my 
uncloned hybridoma cells at a dilution of 1 cell per well or 0.5 cell 
per well.  After about a week I can see colonies growing up in some of 
the wells.  So far so good.  But I notice that in some wells, and only 
in parts of the well, the thymocytes are clumped. So instead of a fairly 
even lawn of feeder cells here and there I will see a clump of feeders 
with a clear area around the clump. Further away from the clump the 
"even" pattern resumes. Does anyone know why this is happening and is it 
something I should worry about??
TIA
Allison