Reddit reviews Leviton 274, Gray, 274-000 Grounding Adapter, 2 Pack

You’re adding a ground to your electrical, it can only make things safer really. Do you have a sliding window? If so just get a flat wire and close the window on it, maybe put some weather stripping in if it gets cold.

Wire it to one of these and then plug in a grounded power strip, and then all of your audio equipment can be grounded.

Leviton 274-000 Grounding Adapter, Gray, 2 Pack
https://www.amazon.com/dp/B000H5WGJ6/ref=cm_sw_r_cp_api_jn9LBbW3JRGRC

I had the same issue for YEARS. Finally solved it with grounding adapters for my monitors and sub. https://www.amazon.com/gp/product/B000H5WGJ6/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

http://www.audioholics.com/home-theater-connection/ground-loops-eliminating-system-hum-and-buzz

you actually want to get rid of one of your grounded cables. Probably from the PC. I used one of these https://www.amazon.com/Leviton-274-000-Grounding-Adapter-Gray/dp/B000H5WGJ6/ref=sr_1_2?ie=UTF8&qid=1496501986&sr=8-2&keywords=ground+plug

except you can often get a 2 pack of them from the local hardware store for like 1 or 2$

Edit: and the plug is not a permanent fix just a troubleshooting method. once you figure out its the ground loop you can take the appropriate measures.

I forgot to mention about the adapters. Japan uses almost the same plug as the US, except they don't have a ground (third prong). There's a good chance your chargers don't use ground either. If that's the case, no adapter needed. If you happen to have something that has a ground, you can get grounding adapter for pretty cheap at a grocery or hardware store.

Japan uses 100V, 50 Hz (east) / 60 Hz (west). Most electronics operate ok in that range, but do check the labels. It doesn't look like you considered it, but don't bother bringing a hair dryer. It likely won't work properly.

You need to ground your amp. First, those outlets look pretty unsafe. You are hearing main line buzz (click the 60 Hz mains hum)

Really what you need to do is get an electrician to rewire the outlet with a proper ground and follow local electrical code. Not doing it is risk of death/electrocution/fire.

However, if it's not an option (e.g., renting or it's cost-prohibitive), you could get away with a plug adapters like the following:

https://www.amazon.com/Leviton-274-274-000-Grounding-Adapter/dp/B000H5WGJ6/

if properly installed (e.g., the junction box is metal and grounded, and so you screw that adapter into the outlet so there's a connected ground). As a last resort if you like to live dangerously, you may be able to clamp an electrical wire to between the adapter ground and a metal water/radiator pipe (again if you are sure there's no non-metal connector anywhere along the pipe), if the pipe is grounded. You probably would want GFCI circuits if you are doing this, because if there is a ground fault (say from a bad appliance being plugged in), you don't want you metal water pipe to suddenly become live and potentially electrocute you and/or start a fire.

Once the outlet is grounded you should test with a ground tester (like $5) and verify you have a real ground and no other issues.

There could additionally be other grounding problems if the wiring in the guitar is bad or the cable is also bad, but you will have bad buzzing if you don't fix the ground first.

EDIT: https://www.youtube.com/watch?v=Nakpj_Mee0Q

https://www.amazon.com/Leviton-274-000-Grounding-Adapter-Gray/dp/B000H5WGJ6/ref=pd_lpo_vtph_60_lp_tr_img_3?_encoding=UTF8&psc=1&refRID=QPYH3493HBC1VEB8HBGF