VST instruments produce unwanted "thumping" artifact

[govnor]

Hi,
I am producing 'piano" music with VSTs. (MDA piano and Proteus X VSTs)

When I bring a VST instrument into Ableton, it produces an unwanted "thumping" sound each time a note is hit. I am experiencing this with all instruments I try.

I have turned down velocity to almost nothing and it still does it.
I have isolated the instrument with no other effects on the track. No EQ, no compression and it still happens.

Since this is very light, piano sounding music, it is very distracting.

I listen to the VST tracks individually with an EQ and push the EQ up to a louder range and you can definately hear a very loud thumping almost all the way across all frequencies.
Any idea what causes this?

I have tried to completely cut off the bottom end of the frequencies where it is most prominent, (I even cut off all sound below 400 htz) and I can still hear it from the upper frequencies.

It kind of sounds like a door slamming in the background of every note played.

I have been trying to fix this problem for months and the time I spent on this one song was enough to produce a whole album.
Please Help!!!

[Ableton_David]

It sounds like perhaps you have too short of an attack on your sounds. Try adjusting the attack on the amplitude envelope within the VSTs.