In electronics, motorboating is a type of low frequency parasitic oscillation (unwanted cyclic variation of the output voltage) that sometimes occurs in audio and radio equipment and often manifests itself as a sound similar to an idling motorboat engine, a "put-put-put", in audio output from speakers or earphones. It is a problem encountered particularly in radio transceivers and older vacuum tube audio systems, guitar amplifiers, PA systems and is caused by some type of unwanted feedback in the circuit. The amplifying devices in audio and radio equipment are vulnerable to a variety of feedback problems, which can cause distinctive noise in the output. The term motorboating is applied to oscillations whose frequency is below the range of hearing, from 1 to 10 hertz, so the individual oscillations are heard as pulses. Sometimes the oscillations can even be seen visually as the woofer cones in speakers slowly moving in and out. Besides sounding annoying, motorboating can cause clipping of the audio output waveform, and thus distortion in the output. Occurrence Although low frequency parasitic oscillations in audio equipment may be due to a range of causes, there are a few types of equipment in which it is frequently seen: Older audio amplifiers with capacitive (RC) or inductive (transformer) coupling between stages. This design is mostly used in vacuum tube (valve) equipment. Motorboating was a problem throughout the era of vacuum tube electronics but became rare as vacuum tube gear was replaced in the 1970s with modern solid state designs, which are direct-coupled. The recent resurgence in popularity of traditional tube-type audio equipment in guitar amplifiers and home audio systems has led to a reappearance of motorboating problems. The problem is sometimes caused in older equipment by the evaporation of the electrolyte from old-style "wet" electrolytic capacitors used in the power circuits of legacy equipment, or in equipment of any age where an amplifier stage is sensitive to feedback via power supply rails, and can be remedied by replacing/upgrading the capacitors. In both old and new designs, even mostly directly-coupled operational amplifier circuits, feedback through the power supply rails can generate ultrasonic oscillations that vary in amplitude at a low frequency (squegging) due to the power supply voltage sagging as oscillations build up (the long time constant coming from the power supply reservoir capacitor) in such a way that the low frequency is audible even though the high frequency fundamental is not.