Unidirectional Signal Spikes?

I am dealing with some sinusoid outputs from devices on an oscilloscope, I am curious as to any ideas people can give me as to why
this is happening.
What could cause unidirectional signal spikes at particular frequencies to show up in the signal. For example, if my cell phone gets too close to the device, it generates spikes. Other circumstances can cause these spikes, so I am interesting in any possibilities or explanations anyone has to offer.
Much appreciation
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RF pickup
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