I am getting a lot of crackling noise on my Uniden TCX805 from all handsets. I have had these phones for a while, buy only recently have I been experiencing the interference. Nothing has changed in my home.

SOURCE: Uniden 5.8 GHz Digital cordless w 3 handsets interference background noise no matter where we are in the house or which handset we use

This is possibly caused by the internet connection.
Try new ADSL filter.
You need one each per device.

SOURCE: Need English documentation for Uniden Sireus 5080 phone & 0500 handsets

Here is the solution I found.
I also bought this equipment and also didn't find anything suitable in the internet, BUT a phonecall to the suplier EUROCOM brought the solution.
I called their service nr. 03-9029000 and got the English user manual as a PDF doc. by email.

Yssachar

SOURCE: uniden 5.8Ghz phone.

You need to reset the main base unit. Unplug the power from the back of the base. While the power is disconnected, press and hold the delete key while reconnecting the power. Wait for a long beep tone. When the display shows 88 or P, press play button one time. If you have a phone without an answering machine, disconnect the power from the back of the base, press and hold find hs button while reconnecting power.

SOURCE: Wifi interference??

The short answer is that it could interfere with the wi-fi, but your wi-fi should not interfere with your phone because it uses WDECT, "wide-band digitally enhanced cordless telecommunications" engineering. No matter how tight the bandwidth is on any RF transmission, power, proximity, and harmonics all play a roll. Ideally we want the power from our transmission to occupy the target frequency but the reality in RF is that this is nearly impossible without DSP filters. I have pasted some extra info below to help answer this question.

Digital Enhanced Cordless Telecommunications (DECT), known as Digital European Cordless Telephone[1] until 1995, is an ETSI standard for digital portable phones (cordless home telephones), commonly used for domestic or corporate purposes. It is recognised by the ITU as fulfilling the IMT-2000 requirements and thus qualifies as a 3G system.


The four most common frequencies today are 900MHz, 2.4GHz, 5.8GHz and DECT 6.0:

900 MHz Currentlythe most common frequency for cordless phones, 900MHz phones may offera greater range than other frequencies. However, the 900MHz spectrum iscluttered and may result in interference with baby monitors and other900MHz cordless phones. Radio scanners can also easily pick up thisband. 2.4 GHz 2.4GHzphones offer better clarity and security than 900MHz, but mayexperience some interference with microwave ovens and wirelessnetworking (wi-fi) products. 5.8 GHz Themost advanced cordless phones available, 5.8GHz phones transmit on anew, open frequency and have the least chance for interference. Theywill not interfere with wireless networking (wi-fi) products. DECT 6.0 DECT6.0 operates on the 1.9GHz frequency. Though newly approved in the US,this frequency has been used for many years in Europe and can increasecall clarity and security. The wi-fi friendly DECT technology easilyintegrates into homes with wi-fi and internet services because the1.9GHz frequency is exclusive to DECT, making it interference free forcordless communications.

SOURCE: I have a Uniden DECT 6.0 phone set. I damaged one

On the base, open the menu and select Register Handset. The display should say Handset Registering.
On the handset you want to register, press and hold # until the handset display says Handset Registering (about 2 seconds).
1.
2.
DSL filterTelephone cordTelephone wall jack
45
In about 30 seconds, the handset display should say Registration Complete. Press Talk/fl ash and make sure you get a dial tone.
If...
Try...
you don't hear a dial tone
the display says Registration Failed --
Making sure the handset is fully charged, then start over at step 1.