Maybe. I've noticed the effect on every metal detector I have ever owned, even the first BFO one I built in 1964. The orientation of the target, it's physical, and chemical makeup, all effect what the detector reports. And, it may be different between detectors, no matter the brand or model. That's part of the learning curve, which is always much more important than the detector itself.
When the effect happens repeatedly, I dig it. The most expensive coin I have ever found (a gold 2 1/2 piece) returned such a signal.
Lastly, even when you dig the target, and it is just junk, rescan the hole! It just may be that another target is under the junk causing the effect.
Alan Applegate