Larry,

 

Is there a vibration source that could alias to low freq?  If the loose
leveling screw increased the effect then maybe that indicates a location
input.  

 

A second thought is your water table or frost level.  In my case the ground
water level comes up to or above my basement floor most spring seasons when
the ground thaws.  I seem to get increased transmission of traffic noise
when the ground is saturated.  When I operated my Lehman I had large tilts
during freezing, thawing and ground water changes.

 

Randy

 














Larry,

 

Is there a vibration source that could alias to low
freq?  If the loose leveling screw increased the effect then maybe =
that
indicates a location input.  

 

A second thought is your water table or frost =
level. 
In my case the ground water level comes up to or above my basement floor =
most
spring seasons when the ground thaws.  I seem to get increased =
transmission
of traffic noise when the ground is saturated.  When I operated my =
Lehman
I had large tilts during freezing, thawing and ground water =
changes.

 

Randy