When I connect two USB devices to my laptop at the same time I get a load of noise.
Every move of the mouse or hard drive on the laptop seemed to result in noise.
If it is a ground loop issue can you suggest something?
It is possible that a ground loop is being introduced in to your system due to a potential voltage difference between the hardware devices, though a ground loop may also be introduced via the laptop's power supply.
You can check this by disconnecting the PSU and running the laptop on batteries for a short time.
You should also ensure that your devices are connected to the same mains ring circuit, as this is another possible cause of ground loops, or narrow down the cause of the loop by removing any other electrical devices that may be connected to the same ring, thereby eliminating any other equipment as the possible cause.
If your laptop, or hardware device that is an intrinsic part of your setup does prove to be the cause, you should be able to resolve the problem by implementing a Ground Loop Isolator. There are many of these available on the market available from major audio electronics outlets.
You may also find the following helpful as another means of resolving this type of symptom:
If ground loops cause problems between hardware devices (but not computers) connect the device audio cable 'screen' at one end only as described below.
Balanced outputs may be connected to unbalanced inputs and vice versa by linking the signal cold (-) to 0V ground as follows:
1. Balanced output to Balanced input - Connect cable screen at destination only.
2. Balanced output to Unbalanced input - Connect screen at source only. Link the -ve output to 0v at the output connector.
3. Unbalanced output to Balanced input - Connect cable screen at destination only.
Link the -ve input to 0V at the input connector.