If you and I have the same definition, blade flutter is caused in a new machine, with good bearings and straight shafts, by an oscillation or harmonic frequency of the blade. The blade itself has its own frequency, which we can hear when you tap a blade lightly with a hammer. Generally, we want as high a frequency as possible to avoid the harmonic frequency. This frequency changes lower as the blade heats; changes higher as the space between the guides or supports is less, and gets higher as the speed increases. Further, we can change the frequency, making it higher, if we tension a blade, usually dome today with a roller that puts a little curve in the blade front to back, but in the past was done by hammering. The amount of curve depends on the speed of the band. Finally, we can add tension to the blade, raising the frequency; tension is added by stretching the blade by moving the wheels a bit further apart.
Blade heating during the cut causes a quick lower of tension and the blade wants to cut wavy. For this reason, wider tooth spacing is often good, and a good feed speed of the log or can’t. This prevents fine sawdust, which can spill out of the gullet and cause heating. To counteract heating, oftentimes cold water, or sometimes a homemade lube, is dribbled aggressively on the tooth edge of the blade.
So, in your case, change the rpms if you can and use cold water on the tooth edge. You might also find that a different blade manufacturer, with different thickness, gullet, spacing, etc. will fix your problem.