11600 is one of those frequencies that can be masked by installation anomalies, either the LNB or the cabling. I recall it being a bugbear of installations years ago on analogue reception, where CNN from Astra 1 could be covered in sparklies unless something was replaced, be it as simple as an f-plug at either end of the run.
On a DiSEqC system there is the additional internal motor circuitry (plus two other connections) that might be causing a poorer signal at this frequency.
Besides the BBC package,whose signal we can check with standard receivers,because they use the usual parameters,the other active frequencies on this satellite are for data transmission.So you will need a device capable of detecting both the signal and the parameters used on these frequencies.And I ask then with what device do you check for anomalies in your reception system? In case there are no signal problems at the BBC,then try a device that knows how to read the parameters(16/32APSK,mode ACM,etc) used for data transmission,such as most transponders used on this satellite. That's what I'd do if I were you.It is true that I have a dvb card and applications that help me determine what problems I have at the reception,whether it's from your reception system(signal attenuation), or from interferences.
In each of the following tests all peripheral equipment has been switched off in the room, apart from the Satlook NIT analyser
OK, first up , imagery of the bands from a fixed 1m dish, connection directly to the LNB. As you can see there is nothing on the opposite polarity or upper band near the frequency of interest (which is white six dots up from the base of the screen)
Lastly another installation on the roof, this time an 80cm reflector on a similar H to H motor. Again the analyser is receiving signal from the LNB through the motor connections. I will double check the analyser imagery for the fourth polarity tomorrow as it is now getting late but you should be able to see the noise from the circuitry within the gearbox is - almost certainly - generating a peak at a single frequency down the incoming cable to the room.