[c-nsp] Input queue flushes and drops

[Javi in AUS]

Gents,

We have a WAN facing Cisco 3845 which is showing the numbers below on it's
Gi0/1 interface:

 Input queue: 0/75/9/71805 (size/max/drops/flushes); Total output drops:
714432


Of course, these counters are increasing and we have a bunch of users at the
other side of the link complaining about poor VoIP performance (they hear
us intermittently although we can hear them Ok).
CEF is enabled globaly, input queue is set to default (75).

GigabitEthernet0/1 is up, line protocol is up
  Hardware is BCM1125 Internal MAC, address is 001b.d37d.f8a2 (bia
001b.d37d.f8a2)
  Internet address is 10.83.2.17/30
  MTU 1500 bytes, BW 20000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 11/255, rxload 10/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is RJ45
  output flow-control is XON, input flow-control is XON
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 3w3d
  Input queue: 0/75/9/71805 (size/max/drops/flushes); Total output drops:
714432
  Queueing strategy: Class-based queueing
  Output queue: 0/1000/0 (size/max total/drops)
  30 second input rate 848000 bits/sec, 634 packets/sec
  30 second output rate 874000 bits/sec, 604 packets/sec
     1146444284 packets input, 1913512714 bytes, 0 no buffer
     Received 1785 broadcasts, 0 runts, 0 giants, 1 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 6993 multicast, 0 pause input
     0 input packets with dribble condition detected
     1121611018 packets output, 2544901813 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out


Should we increase the input queue size to 150,200,250, etc ? Could these
flushed/drops be the cause of the poor VoIP performance?
Many thanks,

P