• If the telephone has the option, put it on mute. Nothing shoud be heard through the handset.
• If there is any line noise, crackling, buzzing, popping or humming, note the time when the test was conducted.
• The test should be repeated several hours later to determine if the noise is present - again noting the time. If no noise is present this time repeat the test at different times, noting if and when the noise is present.

Faults of this kind are caused by a number of different factors - including some that may only occur at particular parts of the day (e.g. when it's light or when it's dark) or during different kinds of weather (windy, rain, storms etc.). Recording this additional detail may also help with your telephone service provider's investigations.
Once the times have been identified when noise occurs the telephone service shuld be contacted to report a fault.

Having the record of the times tested throughout the duration of the fault is useful to ensure any work by the telephone service provider looks at any specific times when the problem occurs.

The 'quiet test' is only carried out by service providers who own the line due to Local Line Unbundling.
As part of the unbundling process to provide Broadband competition in the UK the concept of Local Loop Unbundling (LLU) arose.LLU stands for 'local loop unbundling', which doesn't really give us much information. But put simply, it's a form of technology that allows multiple providers to use a single telecom network.

A 'local loop' describes the wires and equipment that connect your home to the local telephone exchange - also known as the 'last mile'. It's the actual cable through which you receive your landline and broadband. One company (or local authority) is generally the original owner of the local loops, but by unbundling them it can let another provider sell services through the line as well. The companies share use of the physical network, but the exact services they can offer your home can vary.