Ground loops with single ended oscilloscope probes can't be avoided, if the circuit has a protective earth connection (and the oscilloscope too, for electrical safety reasons). But it's a problem in oscilloscope measurement, not in normal circuit operation.
Possible solutions are:
- using a differential probe
- breaking the ground loop by disconnecting one of two protective earth connections (if acceptable according to safety rules)
- breaking the ground loop for AC by a common mode choke, e.g. a toroid core at the probe cable
It should be noted, that high frequency common mode interference are injected in a single ended measurements even without a protective earth connection respectively ground loops. Common mode chokes can partly reduce it, but for sensitive measurements, differential probes are mandatory.