Troubleshooting T1 links

I have 2 T1's that are multilink linked.I am having some input errors and want to see if it is a hardware or link issue. I have read about putting the interface into a loopback state and running some ping test to check CSU\DSU but not sure how to do this with a multilink, The routers I have are Cisco 3640 on both ends with 12.4 IOS.

Router 1
interface Multilink1
 ip address 10.1.10.11 255.255.255.0
 ip helper-address 192.195.192.192
 no ip redirects
 ip directed-broadcast
 no ip proxy-arp
 down-when-looped
 ppp multilink
 ppp multilink fragment disable
 ppp multilink group 1
 service-policy output POLICY1

!
interface FastEthernet0/0
 ip address 192.168.10.11 255.255.255.0
 ip helper-address 192.192.192.192
 ip directed-broadcast
 ip flow ingress
 ip flow egress
 ip route-cache flow
 no ip route-cache cef
 speed auto
 full-duplex
!
interface Serial0/0
 no ip address
 no ip redirects
 no ip proxy-arp
 encapsulation ppp
 no fair-queue
 ppp multilink
 ppp multilink group 1
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/1
 no ip address
 no ip redirects
 no ip proxy-arp
 encapsulation ppp
 no fair-queue
 ppp multilink
 ppp multilink group 1

Router 2
interface Multilink1
 description Multilink to HR
 ip address 10.1.10.10 255.255.255.0
 ip helper-address 192.168.1.70
 no ip redirects
 ip directed-broadcast
 no ip proxy-arp
 service-policy output POLICY1
 down-when-looped
 ppp multilink
 ppp multilink fragment disable
 ppp multilink group 1
 hold-queue 1250 out
!
interface FastEthernet1/0
 description Ace Parking LAN
 ip address 192.168.1.10 255.255.255.0
 ip helper-address 192.192.192.192
 ip flow ingress
 ip nbar protocol-discovery
 ip route-cache flow
 speed auto
 full-duplex
!
interface Serial1/0
 no ip address
 no ip redirects
 no ip proxy-arp
 encapsulation ppp
 no ip mroute-cache
 no fair-queue
 ppp multilink group 1
!
interface FastEthernet1/1
 no ip address
 ip helper-address 192.192.192.192
 ip directed-broadcast
 ip nbar protocol-discovery
 no ip mroute-cache
 shutdown
 speed auto
 full-duplex
!
interface Serial1/1
 no ip address
 no ip redirects
 no ip proxy-arp
 encapsulation ppp
 no ip mroute-cache
 no fair-queue
 ppp multilink group 1

Any ideas?