KDS 19" Avitron Question

My flat screen KDS Trinitron monitor works great except for one thing:

Every now and then a flickering appears about 1 inch from the bottom (a little bit lower than the first tension wire). The flickering is more obvious when it is displaying white background. After some times it usually disappears, only to reappear at a later time.

On very rare occasions this flickering will also appear about 1 inch from the top of the monitor.

Does anyone have experience with this, and what to do about it?

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Athlon T-Bird 900 Mhz
MSI K7T-Pro 2A
128 MB PC-133
64 MB PC-100 (2x)
20 GB Maxtor ATA 33/7200
6.4 GB Maxtor ATA 33/5400
Hercules MX II - 32 MB
HP CD-RW
Pioneer DVD (105-S)
Monster Sound MX300
19" KDS Flat Monitor