This is a common problem of front-loading washers. The drum is rotated in the back by a motor at the bottom of the washer, by way of a drive belt. The belt wraps around a large wheel at the back of the of the drum, and around a small wheel driven by the motor.
When the motor starts spinning, the belt may slip a bit until it comes up to speed. Being rubber, it can make a squeak. Once the belt reaches the speed of the motor, the squeak stops.
Since washers repeatedly change the direction of the drum during the wash cycle, the motor stops and starts each time that happens. So a short squeak may be heard each time the motor starts back up.
Changing the belt is one way to eliminate the squeak, but it can come back after a short period of use. Such belts can develop a glazed surface (smooth & slick), causing them to slip a bit. A more lasting solution is to spray belt dressing on the belt. Belt dressing coats the surfaces of the belt and the drive wheel, making them tacky, increasing friction, and reducing slippage.
In my own washer, there are large holes on either side of the back panel that can be reached by leaning over the washer, or climbing onto the top. (Depending on how tall you are.) This way I can spray dressing onto the belt, without sliding the heavy washer away from the wall, and then disassembling the back panel. This isn’t an ideal solution, as much of the dressing ends up on the back of the drum rather than on the belt. But the dressing won’t harm the drum, so I don’t worry about that. Dressing could hypothetically get into the drum’s rear bering, causing premature failure. But the bering should be sealed, and I don’t spray dressing directly on it anyway. I suppose it might be possible to get dressing into the motor itself, ruining it. But again, I don’t spray dressing toward the motor or near it, so that shouldn’t happen. ??One last caveat: The controls on my washer are on the front of the machine, far away from the belt. If the controls of your own washer are on the back, be careful not to spray dressing anywhere near them.