I agree. Your scanner's lamp is definitely flickering during the scan.
Are we scanning a print or a transparency? If this is a print, the problem is inside the scanner chassis. If it is a transparency, the problem might simply be in the connection between the lid and the chassis.
Scan both, transparency and print, and see if the problem occurs in both modes. A failure in BOTH modes indicates the internal power supply for the cold cathode lamp is failing. There is little you can do to repair that.
If the problem is in the transparency lid, my first line of attack would be to check the connection between the lid and the scanner body.
If it is the type that can be unplugged, unplug it and inspect it for damage. Check both the plug and the socket. Look for damaged contacts, frayed wires and foreign materials or dirt. Carefully clean the contacts with an appropriate tool, being careful not to cause your own damage in the process. Plug it back in, being sure the contacts are fully seated.
Check the wire, itself for damage. Look for broken insulation, wires that are pulling out of the strain reliefs where the wire enters the chassis at both ends, twisted cables or any other visible damage.
Rectify these problems, if they exist, then retest.
If you know how to use a soldering iron, you MIGHT be able to repair damaged wires if you are careful. Remember! This is a high voltage connection! There could be several hundred volts going through those wires! Be sure the scanner is powered off, unplugged from the mains and has bee sitting idle for at least 30 minutes.
If you know somebody who is handy with electronics and can effect the repair, you might be able to get this done for the price of a few beers.
I also agree with Loris... Contact Canon for service but don't spend more than $50 (US) to get this repaired. (I assume this is an out-of-warranty repair. Correct?)
A new flatbed scanner can be had for $150 - $200 (US).
The CanoScan 8800F uses LEDs instead of a cold cathode lamp. It has zero warm-up time and will never have trouble with the lamp failing like you have had. I use this scanner and it is good for me.
But, as Loris indicates, shop around. There are similar models from several manufacturers. Definitely consider Epson. Good brand.