Fender Twin Hum Hum Hum

[teepeeasel]

When my amp is turned ON it has little bit of hum but when I connect my Fender Strat (mexican) it hums and hisses and what not, its bearable in some ways but when the amp is cranked its loud. I also notice when I touch anything thats metal on the guitar the hum dies down a little and when I let go of the guitar it hums. Any reason to this and how I can solve this problem?

[Fragger]

Do all guitars played through the amp hum like the strat?

[booj]

Is the amp grounded properly?

[Zipslack]

Check the guitar

My first guess would be bad or improper grounding on the guitar. Check that the wire is soldered properly to the tremolo spring claw. If it's okay, you'll need to start looking at the other electronics. Start with the input jack and make sure the ground/shield wire is connected. If that's fine, then pull the pickguard and check for the ground connections to the pots. There's bound to be a ground connection that's come loose or wasn't soldered properly. My guess would be the wire to the cable jack, just because those break loose fairly often. If the guitar checks out okay, and it does NOT do that on a different amp, then start checking the amp for grounding issues.

[teepeeasel]

All the wirings are good. I noticed that the inside cavity has no shielding and neither does the pick guard, perhaps that can be an issue too? Im not exactly sure how to check the grounding on the amp, may you give me some advice on how to check, please? thanks.

[Gibsonman63]

Humbucking

Try plugging a guitar into your amp with humbuckers if you have one available. If this reduces your problem significantly, then it is time to consider some modifications to your strat.

[chipprogr]

Is your amp the red knobed "the twin" or a twin reissue, original twin? please specify what age the amp is. THanks

[oc disorder]

Hi Teepeeasel !
This is a common problem with Strats.
There will always be a small amount of buzz especially with high gain settings or using a boost or distortion stomp box .
Its usually more noticeable at home or in a quiet environment than when playing live.

"I'm not exactly sure how to check the grounding on the amp"
The metal chassis of the amp should be connected to the earth pin of the power plug.
The quickest and easiest way to check is to measure the resistance with an multimeter on the ohms scale or using the continuity test if it has one (it beeps if the connection is good).
By putting one probe on the chassis and the other on the power plug earth pin there should be hardly any resistance (maybe 1 ohm) depending on how well you connect and the accuracy of the meter.
You could also visually examine it - if its a removable power plug check the screws are nice and tight as vibration can sometimes undo them.

"I noticed that the inside cavity has no shielding and neither does the pick guard, perhaps that can be an issue too?"
Usually the hum/buzz coming from the guitar can be tamed by shielding and as you have observed a lack of it maybe you should consider getting a kit or some sticky backed copper foil to help reduce it.
If the internal wires are not shielded (like a guitar cable is) this will add significantly to the problem.
Do a search especially in the guitar tech section or search on the web for guitar cavity shielding.
The pickups may benefit from shielding also.
Fluorescent lights can generate interference as can light dimmers which the guitar can unfortunately pick up.

You may notice when you stand close to the amp particularly near the power transformer there can be a lot of hum as the pickups are in the radiated field of the transformer.
By changing the angle of the guitar standing in a different position you can usually find a quiet spot.

"I also notice when I touch anything that's metal on the guitar the hum dies down a little and when I let go of the guitar it hums."
Well I suggest that you hold on to it while playing it......seriously, your body is acting like a shield when you are touching the metal parts, your body is at ground potential which helps reduce the noise the guitar is picking up.

As Zipslack said check that wire that runs from an earth point in the guitar to the vibrato arm block which in turn grounds (or earth's) the strings.They also help to reduce noise acting like a shield.
Usually this kind of problem is a combination of a number of minor issues that all add up rather than one main fault.

Gibsonman63's advice will help you get a better idea of the issue if you have access to a humbucking guitar, at least it will help eliminate the amp out of the equation.