On the K6 Sennheiser there is a switchable bass roll-off filter and flat. l have been using the flat for Interviews. and been getting some back ground noise and a little rumbling as well.
If l switch to the bass roll-off filter, would this help remove?

Thanks, Ron

Yep, that's what it's for. It'll cut below the range of most vocals.

Thanks Steve

The bass rolloff switch on the k6 has an unusually high knee point. I don't remember precisely what frequency it's rated at, but it does have a more pronounced effect than the more common 80 hertz on some other mics.
Be sure to listen to the difference between settings and if the K6 switch makes your sound too thin, search for different ways in your audio chain to accomplish the reduction of bass frequencies or the pickup of rumble.

Thanks for your in put Jay.

You can see the effects of the bass roll-off switch HERE (http://www.sennheiser.co.uk/uk/icm.nsf/resources/C1256F140044E469C1256F4E004FF727/$File/03279_fg.jpg).

It is -3dB at 300Hz and -12dB at 100Hz.

This is below speech frequencies and should take out wind and rumble nicely - this is what it was designed for.

I can certainly hear the effect of -3db down at 300 hertz on voice. That's why I only employ the K6 rolloff in extreme cases, usually relying on the low cut or EQ on a mixer instead. Plus I'm using a Lightwave Equalizer for wind protection and a good shockmount, both of these decrease the need for rolling off the bass. So again, listen in your situation and determine whether the switch is a necessity or whether it's too much rolloff.

The K6 roll off is pretty agressive, but it also makes the mic a lot more directional. I use it all the time with that mic.