I have a set of beovox S30 speakers and they  and woofer surrounds are rubber showing no signs of deterioration. I have not changed the capasitors, but I am planning to. These speakers are my first B&O which I bought with the Beocenter 2800 back in 1978. I like the sound of these speakers but:

One of them sounds OK but the other has a BUZZZ with the bass sound of about middle volum and up. It sounds like there is some part is loose inside. I have open it up and I can't see anything. When I ut my finger lightly inside the  woofer or at the back the buzzing stops and it sounds OK.

What could this be and is it possible to fix? 

There are two types of Beovox S30 (6301/6317).
What you describe is a common problem on the type 6301.

The spider has loosened from the metal chassis.
In some cases, where only a small part of the circumference has
loosened, it can be glued back but in worse cases the woofer will
have to be replaced. The tolerances between the magnet and
coil is pretty tight in this type of woofer and it's
practically impossible to center the coil and spider again if
its lose along too much of the circumference.
I have good used woofers in stock if you need.

The above applies to Beovox S30 (type 6301) and Beovox P30 where the same type of woofer is used.

Martin

Dillen:

There are two types of Beovox S30 (6301/6317).
What you describe is a common problem on the type 6301.

The spider has loosened from the metal chassis.
In some cases, where only a small part of the circumference has
loosened, it can be glued back but in worse cases the woofer will
have to be replaced. The tolerances between the magnet and
coil is pretty tight in this type of woofer and it's
practically impossible to center the coil and spider again if
its lose along too much of the circumference.
I have good used woofers in stock if you need.

The above applies to Beovox S30 (type 6301) and Beovox P30 where the same type of woofer is used.

Martin

 Thanks again Martin, I will check them this weekend which type it is.

Dillen:

There are two types of Beovox S30 (6301/6317).
What you describe is a common problem on the type 6301.

The spider has loosened from the metal chassis.
In some cases, where only a small part of the circumference has
loosened, it can be glued back but in worse cases the woofer will
have to be replaced. The tolerances between the magnet and
coil is pretty tight in this type of woofer and it's
practically impossible to center the coil and spider again if
its lose along too much of the circumference.
I have good used woofers in stock if you need.

The above applies to Beovox S30 (type 6301) and Beovox P30 where the same type of woofer is used.

Martin

You were wright Martin the type was 6301. I have tried to see if it was something loose under heavy light but I did not see anything. How difficult would it be for me to change with a used woofer. What shall be done with the old woofer. Is it a good Idea to change Capasitors  while I am at it the speakers are 29 years old. PM me about the kit and woofer, please

You need to put a finger in through the holes in the chassis and gently lift the cone a bit.
I'm sure you'll see that the spider has losened from the chassis.
Please see the attached photo.
Maybe you can repair the old woofer, if not the old woofer
is practically worthless and you'll have to replace it.

New capacitors is always a good idea, a kit is available. 

You need to do a couple of solders when replacing the woofer and/or caps and of course unscrew the woofer/filter.

Martin