I've struggled to find an answer to this online and only found one article that also agreed.

Does anyone else find, that drinking beer when having a longer moustache makes the beer taste very metallic and not very nice?

When I drink directly from a bottle and the beer doesn't touch my moustache it's fine/tolerable. The minute it's in a glass and moustache acts like a filter it's not good

Anyone else notice this or know what the cause is?

The one article I found which supported this point was one person in a forum saying they had the same issues apparently they were saying its the beer touching the hair which causes a reaction resulting in a metallic taste - but no idea how or why