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I owned a transmission shop for 15 years. On multiple occasions a customer would show up with shifting problems, multiple makes & models. After installing the latest thumping stereo there were problems ranging from erratic shifts, slipping, limp modes and outright failures. It turns out that spikes in power draws (heavy base notes, raucous lead guitars) would initiate pulse waves in the systems, imitating pulse width modulation signals. After some diagnostics and occasional ecm replacements, some were able to overcome the problem by installing a large shunt on the stereo power circuit but not always.