Strange Knocking Sound Coming From Tank?

[stanleo]

Its the weirdest thing. We have all heard it. The knocking comes from one corner of the tank and sounds like two rocks clanking together. There are no lose rocks and I can't see anything that could be making the noise. Its in the corner with the heater and one of the canister filters (Fluval 304) intake/outtake and a small powerhead that blows over a piece of driftwood that the 2 bamboo shrimp perch on. Its not constant and has no discernible pattern. It will start up suddenly and go on for a while, stop just as suddenly with no noticeable changes but sometimes stops when I go to look for the source of the sound and when I walk away it sometimes starts again. The tank inhabitants are:
 
1 angelfish
4 pearl gouramis
9 harlequin rasporas
6 flame tetras
15 corys (5 sterbai, 5 peppered, 5 false julii)
1 clown pleco
5 otos
2 dojo loaches
1 betta
1 viper shrimp 
2 bamboo shrimp
2 mystery snails
about 20 assassins snails 
100's of MTS 
 
Anybody have any theories? Right before it started I did add one of the bamboo shrimp, a new cabomba plant and some sagatarius but I can't imagine it could be coming from one of those. 

 

[AmtotheBurr]

The shrimp must want out of the tank and keeping knocking trying to find a door hope you figure it out, it would be driving me insane

 

[gmc1]

I have had this.possible mts in cannister?

 

[Akasha72]

I hear the odd knock from mine too. I've never worked out what it is either
did wonder if it's to do with the heater though

 

[Byron]

I would suggest it may be the loaches.  If I could hear the sound I might be able to confirm this, but generally speaking my Botia kubotai can make quite a clicking sound that I could describe similar to the way you have.  This occurs frequently when they are eating, such as breaking apart tablet food.  It is also used in communication when interacting (all loaches are highly social fish).  This might be what you are hearing from your dojo loaches.
 
Byron.

 

[Munroco]

I'd suspect the filter, maybe an outlet pipe vibrating against something or bearings (or whatever is inside filters) giving up the ghost?

 

[nic1]

Hi Im with Byron on this one, I have 3 weather loaches and they are ususally the 3 naughty culprits in my tank, they uproot plants and swim under anything they can fit through, if the space is too ssmall they squeeze them seves through destroying anything thats in their path! my vallis has been uprooted loads of times and I just let it float now!
Any way, they surf under the sand and under my drift wood that wobbles when they are playing near it. this may be the case here with you... funny little things.

 

[Akasha72]

Byron ... do you know if SAE's make this sound? Could that be what I'm hearing? Or perhaps is them banging into things now they are sooo big!
 
My cories sqeak occasionally and I've also read that oto's can squeak too. 

 

[Byron]

Byron ... do you know if SAE's make this sound? Could that be what I'm hearing? Or perhaps is them banging into things now they are sooo big!
 
My cories sqeak occasionally and I've also read that oto's can squeak too. 

 
I've no idea on the SAE.

 

[Akasha72]

okay, no worries

 

[Bazouteast]

I have had this.possible mts in cannister?

What does "mts in cannister" mean?

 

[Bazouteast]

Byron ... do you know if SAE's make this sound? Could that be what I'm hearing? Or perhaps is them banging into things now they are sooo big!
 
My cories sqeak occasionally and I've also read that oto's can squeak too. 

...and what are SAE's please....

 

[Akasha72]

MTS - Malaysian Trumpet Snails.
Canister - External filter
SAE - Siamese Algae Eater (fish)

 

[ShinySideUp]

SAE --Siamese Algae Eater
 
Loaches make a clicking sound when they are eating, they are firing jets of water from their mouths at the food to break it up. I have an occasional knocking in my tank which sounds nothing like loach-clicking, it is caused by the lid of my small in-tank filter not being closed properly and is knocking in the current; the noise seems like a hollow clunk rather than higher-pitched loach-clicking.

 

[Akasha72]

my tank makes most of the knocking noises on a night after the tank lights have gone out. I wonder if it's a heat thing ... things cooling down? the tubes get really hot