How much noise is to be expected on a phone line?

[#1]

I don't typically keep a landline phone plugged in, but doing a 17070 quiet line test I can hear a low-level hum.

It sounds about 50hz at a guess, but I'm not 100% confident whether it's an earth hum, RF noise or something else. I'd describe the volume as quiet but clearly noticeable: drowned out by a dial tone, and not enough to impede conversation, but definitely there.

Phone is a corded BT handset plugged directly into the lower half of my two-port master socket, with the VDSL modem plugged into the upper half. No other phone wiring in the house. Problem is still present and identical with the VDSL modem disconnected and the handset plugged directly into the test socket. 

I've ran through the automated phone troubleshooter (https://www.plus.net/my-account/tools/phone-troubleshooter/) which didn't identify a fault.

I guess my question is about what level of background hum is a) acceptable and normal for a phone line, and b) whether this noise is likely to impact my VDSL speeds. I'm in the process of upgrading to 80/20 and live within spitting distance of the FTTC cabinet so I'd expect near-optimum speeds, but I don't want to go down a wild goose chase.

[#2]

@ChrisFox  Welcome to the forum.

 If it’s really 50Hz (or 100Hz as hum usually is) then it’s way outside of the broadband frequency bands so should not cause any problems. I would say just wait and see.

[#3]

Hi Chris, I don't know if your phone hum will affect your BB though any interference can affect its performance but you won't know until it's installed!

I had a similar problem on ADSL eight or nine years ago when I was getting about 6MB (I'm 3km from the exchange) and also had a faint hum on the phone. Our house was built in 1969 and still had the 1960s pattern small junction box beside the front door where people used to keep their phones on a small telephone table (that dates me doesn't it).

The incoming line is 25m of steel-cored overhead cable to the gable wall, from which I traced it inside the eaves soffit to above the front door where it went through the wallplate. When I looked in the loft I found the BT installer had left at least 10m of cable neatly coiled above the consumer unit ... you couldn't arrange a better means of picking up mains interference. It might be worth investigating your own incoming line.

Yes, I did fix it -- very naughtily. When I removed a soffit panel I spotted an unauthorised non-BT jointbox presumably made during re-roofing before we bought the house. I unscrewed the incoming cable and its box, pulled it back to its origin and fed it through a hole I had bored into the loft, where I joined it using the same box to a high-quality twisted pair leading to a new NTE5 master socket in our home office. The result was a 25% improvement to around 8MB and no hum on the phone. Today we enjoy 35/36MB on PN fibre at 300m from the cabinet. The surplus cable coil is still lying in the loft though after 50yrs BT is hardly likely to collect it.