diff --git a/src/audio.h b/src/audio.h
index e48c7066d..b61fda3aa 100644
--- a/src/audio.h
+++ b/src/audio.h
@@ -161,25 +161,6 @@ void audioDefevent(uint8_t e);
 #define AUDIO_MIX_WARNING_1() audioDefevent(AU_MIX_WARNING_1)
 #define AUDIO_MIX_WARNING_3() audioDefevent(AU_MIX_WARNING_3)
 
-#if defined(PCBSTD)
-#define AUDIO_HEARTBEAT() \
-  if (audio.toneTimeLeft > 0) { \
-    static uint8_t toneCounter; \
-    toneCounter += audio.toneFreq; \
-    if ((toneCounter & 0x80) == 0x80) \
-      PORTE |= (1 << OUT_E_BUZZER); \
-    else \
-      PORTE &= ~(1 << OUT_E_BUZZER); \
-  } \
-  static uint8_t cnt10ms = 77; \
-  if (cnt10ms-- == 0) \
-    cnt10ms = 77; \
-  else \
-    return; \
-  audio.heartbeat()
-#else
-#define AUDIO_HEARTBEAT() \
-  audio.heartbeat()
-#endif
+#define AUDIO_HEARTBEAT()   audio.heartbeat()
 
 #endif // audio_h
diff --git a/src/open9x.cpp b/src/open9x.cpp
index 4269c3ca0..e528c5136 100644
--- a/src/open9x.cpp
+++ b/src/open9x.cpp
@@ -1776,7 +1776,23 @@ ISR(TIMER0_COMP_vect, ISR_NOBLOCK) //10ms timer
 
   sei();
   
-  AUDIO_HEARTBEAT();
+#if defined (PCBSTD) && defined (AUDIO)
+  if (audio.toneTimeLeft > 0) {
+    static uint8_t toneCounter;
+    toneCounter += audio.toneFreq;
+    if ((toneCounter & 0x80) == 0x80)
+      PORTE |= (1 << OUT_E_BUZZER);
+    else
+      PORTE &= ~(1 << OUT_E_BUZZER);
+  }
+
+  static uint8_t cnt10ms = 77; // execute 10ms code once every 78 ISRs
+  if (cnt10ms-- == 0) { // BEGIN { ... every 10ms ... }
+    // Begin 10ms event
+    cnt10ms = 77;
+#endif
+
+    AUDIO_HEARTBEAT();
 
 #ifdef DEBUG
     // Record start time from TCNT1 to record excution time
@@ -1801,6 +1817,10 @@ ISR(TIMER0_COMP_vect, ISR_NOBLOCK) //10ms timer
     g_time_per10 = dt2 - dt; // NOTE: These spike to nearly 65535 just now and then. Why? :/
 #endif
 
+#if defined (PCBSTD) && defined (AUDIO)
+  } // end 10ms event
+#endif
+
   cli();
 #if defined (PCBV4)
   TIMSK2 |= (1<<OCIE2A);