Roland 150 amp makes a buzz sometimes. But cables are fine

1. Check the power cable and ensure it is securely connected to both the amp and the power outlet. 2. Check the fuse and replace it if needed. 3. Check the power switch and ensure it is in the correct position. 4. Check the battery (if applicable) and replace it if needed. 5. If the amp is still not turning on, contact Roland customer service for further assistance.

You have a ground problem. I suspect your cord. Replace it, being sure you use an instrument cable, and see it that doesn't help.

Best bet is to contact Roland support directly. Here's the link-
Roland Company Contact Us

Try different cables. That would be the most simple and cheapest fix.

This is often caused by poor earth lead connections or pour quality screen cable being used to the inputs of the amp input.

Make sure the power supply for this is powered from the SAME receptacle as your amplifier is powered. Keep the cable from this to the amp fairly short and high quality cable. Keep guitar away from magnetic field sources... the wall wart adapters are notorious for generating magnetic fields.

When you turn it on does the speaker thump or make a hissing sound? If so then the speakers are ok. If there is notany sound, you must measure the speakers to make sure there is continunity.
If you need further help you can send it to Pro Line Music.215-736-8055

If this ties to a keyboard, make sure the keyboard and this are BOTH plugged into the same receptacle. You should send a higher level from the keyboard (turn volume up to around 70% or so) and use less volume at the input gain of this amp. Use more at master volume if the amp has one if needed. If the hiss is there with NO input cables plugged in and input gains at 50%, that is objectionable, the amp probably needs servicing. Unused channel gains should be clear down.

First thing is to determine if sound is from the speaker or possibly the cabinet. If from the cabinet it is likely the power transformer is vibrating the chassis. This sometimes can be cured by adjusting the mounting bolts.
If the sound is from the speaker, then an electronic "cure" is needed. Please note that a very quiet hum is normal but if you can hear it 5 foot away, that is un-normal.

The hum would probably be due to failing component in the power supply. Unles you are adept at electronic repair, best to take it in for servicing.

MAKE sure you have it connected to a three wire circuit that has the ground. A lot of these style amps will buzz if they are left ungrounded.

Also search for sources of buzzing light light dimmers.

Further, power supply electrolytic filter caps are suspect.