I don't believe the screen settings shown by essexboy have any effect on the creation of the mdmp files as that is the manual generation of a support package, not any crash dump files.
So I can't see a way of disabling the crash dumps.
I would suggest starting a support ticket and or possibly uploading a selection of these recent mdmp files zipped to the avast ftp location for analysis.
Give the zip file you are uploading a unique name (e.g. forumusername-mem-dump.zip, etc), so they can identify it. It might not be a bad idea to create a text file (readme.txt) with any relevant information,
avast topic URL, user name, etc. etc. in the zip file. Not to mention posting the name of the file you uploaded in the topic, this acts as another searchable reference.
Upload the zip file to the ftp server
ftp://ftp.avast.com/incoming, you don't have read permission for this location so you won't see the uploaded file.