Is this a tubshower combo or shower only? Do you have the make and model of the control? Is it a single handle control or two or three handle control? Do you use shampoo with conditioner or just regular?….just kidding!
Sorry for all the questions but these answers would help those of us here to narrow down the problem…..maybe!
Just check around the control valve and see if there is a makemodel number. If not, you might even describe its appearance a little.
One more thing, if this IS a tubshower combo unit, tell us where the shower diverter button or control is located. Some are operated by a separate handle, some are operated by a “push in” button near the main control valve and still others are located at the spout(either a pull “up” knob or even a pull “down” knob incorported into the end of the spout). These last are notorious for causing a high pitched squeel if they do not seal off properly.